Automatic dishwashing detergents constitute a generally recognized distinct class of detergent compositions whose purpose can include breaking down and removing food soils; inhibition of foaming; promoting the wetting of wash articles in order to minimize or eliminate visually observable spotting and filming; removing stains such as might be caused by beverages such as coffee and tea or by vegetable soils such as carotenoid soils; preventing a buildup of soil films on wash ware surfaces; and reducing tarnishing of flatware without substantially etching or corroding or otherwise damaging the surfaces of glasses or dishes. The problem of glassware surface corrosion during washing the cycle in the automatic dishwashing process has long been known. Current opinion is that the problem is the result of two separate phenomena. On one hand, the high pH needed for cleaning causes silica hydrolysis. This dissolved silica/ate (together with silicates added purposely to prevent china and metal corrosion) deposit on the glasswaresurface leading to iridescence and clouding. On the other hand, builders cause corrosion. The builders will chelate metal ions on glassware surfaces, which results in metal ion leaching and renders a less durable and chemical resistant glass. After several washes in an automatic dishwashing appliance, both phenomena can cause significant corrosion damage to glassware surfaces such as cloudiness, scratches, and streaks that results in consumer dissatisfaction.
Most consumers agree that corrosion of glassware surfaces, resulting from use of automatic dishwashing (ADW) appliances, is one of their most serious unmet needs. One approach to reducing glassware surface corrosion is to provide corrosion protection agents comprising water-soluble metal salts (such as zinc salts of chloride, sulfate or acetate) to afford some measure of glassware surface protection. Another approach is reduce precipitate formation, caused by the introduction of soluble zinc salts in a high pH environment, by spraying a solution of the water-soluble zinc salt onto granular polyphosphate particles. Another approach is to combine soluble zinc and a chelant. Another approach is to use insoluble zinc salt to control the release of Zn2+ ions in the rinse to avoid filming. Another approach is to provide an automatic dishwashing composition with a mixture of disilicate and metasilicate. Another approach is to provide an additive to an automatic dishwashing composition, such as, a copolymer of an organomineral siliconate, which is obtained by condensation polymerization of an alkali metal disilicate and an alkali metal siliconate. Another approach is to provide an alkali metal silicate partially substituted with calcium, magnesium, strontium or cerium as a counterion. Another approach is the use of metal salts, particularly of aluminum, wherein the metal salt is sequestered to form a metal salt-sequestrant complex, such as, an aluminum (III)-sequestrant complex. In yet another approach, a fast-dissolving aluminum salt is used but this aluminum salt is combined with greater than about 10 wt. % silicate in high alkalinity products.
Thus, while there are many approaches available, there is still a continuing need to develop alternative methods of reducing glassware surface corrosion using corrosion protection agents such that significant glasscare benefits are achieved yet the problem of glassware surface corrosion is reduced.